1. Field of the Invention
The present invention relates to a magneto-optical recording medium on which information is recorded or erased by utilizing a rise in temperature of the medium by a laser beam and information is reproduced by utilizing a magneto-optical effect.
2. Description of the Related Art
A magneto-optical disk is known as a rewritable high-density recording medium, and an increase in information quantity gives rise to a desire for higher densities of the medium. Further, various methods have been proposed as magneto-optical recording methods in the next generation, and the requirement to the quality of the recording medium has been further increased. The magneto-optical recording medium is required not only to allow its production at low costs with simple steps, but also to allow a high signal quality and high reproduction stability.
A rare earth-transition metal amorphous alloy film such as TbFeCo or GdFeCo is used as a magnetic recording film constituting the magneto-optical recording medium. However, such a magnetic film has a defect that its characteristics are prone to be deteriorated by oxidation or the like. To cope with this, the magneto-optical recording medium generally has a structure that a first dielectric film, a magnetic film, and a second dielectric film are laminated together in this order over a transparent substrate. In some case, a metal reflective film is further laminated on the second dielectric film. Thus, the magnetic film is sandwiched between the first dielectric film and the second dielectric film to thereby prevent moisture contained in the substrate and oxygen or the like in the atmospheric air from reaching the magnetic film, thus suppressing the deterioration of the characteristics of the magnetic film.
Further, as the first dielectric film is provided between the substrate and the magnetic film, the multiple interference effect (Kerr enhance effect) of a laser beam utilizing a difference in refractive index between the substrate and the first dielectric film can be exhibited to thereby apparently enlarge the Kerr rotation angle of the magnetic film, thus allowing a high reproduction output to be obtained in reading information. In a conventional magneto-optical recording medium, the first and second dielectric films are formed from the same kind of materials. For instance, the first and second dielectric films are formed from silicon nitride (SiN) or aluminum nitride (AlN).
It is known that when stress is applied on a magnetic body, perpendicular magnetization anisotropic energy is accordingly generated in the magnetic body. If this property is applied to magnetic recording or magneto-optical recording, the properties of the magnetic film may be controlled, and recording medium greatly superior in characteristics to the conventional recording medium may be produced even with use of the same magnetic film as that in the prior art.
In Japanese Patent Laid-open No. 4-13869, there is disclosed a film forming method for a magneto-optical recording medium wherein an Ar gas pressure is increased in forming a recording magnetic film to thereby enlarge internal stress in the magnetic film. The enlargement of the internal stress in the magnetic film is intended to improve carrier-to-noise ratio (C/N). However, the Ar gas pressure of the film forming conditions described in this publication is high such as 10 to 100 mTorr, causing instability of discharge during sputtering. As a result, a good-quality magnetic film cannot be obtained.